Infrared thermometers for determining body temperature have been in use for several years. Among the most widely known are infrared thermometers for measuring the temperature in a person""s ear. Such an infrared thermometer is known from EP 0 388 463. It includes an infrared radiation sensor measuring the infrared radiation emitted by the measurement site, and an ambient temperature sensor measuring the temperature of the radiation sensor. The signals of both sensors are needed for determining the body temperature. Considering that the ear is readily accessible while at the same time affording reliable protection from external impact, accurate body temperature readings can be generally provided with this arrangement. However, in view of the temperature gradient in the ear canal, the measured temperature depends on how the thermometer is manipulated. This presents a problem particularly with small children where the probe of the thermometer does not fit into the ear canal because of the probe""s relatively large diameter. Additional inaccuracies that may occur are attributable to the presence of cerumen in the ear canal or the use of contaminated protective covers.
Also commercially available are infrared thermometers which are suited to temperature measurement in the axilla or on the skin surface. Where body temperatures are taken in the axilla or on the forehead or in the temple region, measurement inaccuracies due to external impact are a frequent occurrence. Clinical tests have revealed that the differences to oral or rectal readings are greater here than the temperature measurement in the ear.
An infrared thermometer marketed under the designation National DM-T2S or BDM-T2A includes several detachable probe heads possessing differing outside diameters. The thermometer therefore has only a radiation inlet opening and a device for attaching the probe heads, making it necessary to select the appropriate probe head prior to a temperature measurement.
It is an object of the present invention to provide an infrared radiation thermometer and a method permitting the body temperature to be determined from readings taken at different sites on a person""s body.
The present invention relates to an infrared thermometer which is suited to body temperature measurements at different sitesxe2x80x94including, for example, a person""s ear, mouth, forehead, skin, temple, rectum or axilla. In contrast to contact thermometers for oral, rectal or axillary measurements, the infrared thermometer requires however that it be adapted to fit the particular measurement site. A measurement in the ear necessitates a probe head that is sized to fit the ear diameter. In addition, the use of protective covers is advantageous in this case.
For measurements on the skin surface, for example, on the forehead or on the temple, means are advantageously provided in order to minimize errors introduced by reflection of infrared radiation on the skin surface. One possibility involves shielding of the measurement site and back-reflection of infrared radiation by means of a suitably shaped mirror. However, the mirror may be dispensed with if the measurement site is shielded by the probe head such that the radiation component reflected by the skin emanates from the probe head itself, rather than from the environment. By means of the known probe head temperature it is then possible to correct the measured radiation temperature correspondingly. During a measurement on the forehead or temple it is wise to scan a major area, meaning that the thermometer is moved across the skin surface, and to use the maximum temperature value measured during this manipulation for further calculation of the body temperature. A protective cover is not absolutely necessary for such measurements on the skin.
A thermometer of the present invention includes in a manner known in the art an infrared radiation sensor and an ambient temperature sensor. In the method of the present invention the body temperature T indicated by the thermometer is calculated in dependence upon the measured ambient temperature Ta which has a strong influence particularly on the skin temperature, the temperature Tb determined by radiation measurement in a manner known in the art from the signals of the ambient temperature sensor and the radiation sensor, and parameters determined during the prior calibration of the thermometer. To be able to compare the temperature readings taken at different locations on the body properly, the provision of an oral, rectal or core temperature equivalent by means of a corresponding calculation is appropriate. The body temperature T is calculated, for example, by applying the formula given below where d0, d1, d2, d3 and d4 are the parameters identified. This formula enables, for example, also the radiation component reflected by the skin to be taken into account. The non-linear influence of the body temperature on the skin temperature or the temperature in the ear canal can be taken into account by the parameters d3 and d4. This is advantageous because for a patient running a high temperature the then improved blood flow makes the surface temperature of the body less strongly dependent on the ambient temperature than for a person running no temperature:
T=Tb+d0+d1(Tbxe2x88x92Ta)+d2(Tbxe2x88x92Ta)2+d3(Tbxe2x88x92Ta)(d4xe2x88x92Tb)